The present invention relates to a method and apparatus for oxygen-cutting pieces of steel, such as slabs, billets, and blooms.
The technical background can be illustrated by document EP-A-0 639 416 which describes a two-line oxygen-cutting installation, each line comprising a moving carriage having a pendulum type oxygen-cutting torch. Reference can also be made to document U.S. Pat. No. 2,820,420 which describes an oxygen-cutting torch cantilevered out from a carriage that can be moved horizontally, and to document WO-A-96/20818 which describes a traveling crane supporting a telescopically-extendable vertical working arm.
In general, conventional oxygen-cutting torches are constituted by two main portions, namely a first portion for delivering fluids (oxygen, fuel gas, cooling liquid), which portion is referred to the torch body, said portion not coming directly into contact with the flame, and a nozzle-forming second portion which does come directly into contact with the flame and which serves to spread and dispense the fluids and to eject the gases (fuel and oxidizer) with specific proportions and characteristics specific to fluid mechanics for the purpose of achieving the desired oxygen-cutting operation.
The person skilled in the art knows that oxygen-cutting nozzles can perform two functions simultaneously: the first function consists in producing a heating flame by supplying and mixing (outside or inside the nozzle) a fuel gas and an oxidizer gas, such as oxygen, for the purpose of raising the cutting edge zone to very high temperature so as to cause the metal for cutting to enter into spontaneous combustion on arrival of a separate jet of oxygen. The second function consists in producing and directing a specific jet of oxygen on the zone that has already been raised to spontaneous combustion temperature so as to cut the metal with desired geometrical characteristics. For this purpose, existing oxygen-cutting nozzles have one or more cutting oxygen ducts, that are optionally parallel, situated in a common plane (generally orthogonal to the cutting surface of the piece to be cut), together with a certain number of heating ducts which are arranged either concentrically around the cutting jet of oxygen, or else on either side of the travel direction of the cutting jets of oxygen.
The oxygen-cutting nozzles used in traditional techniques are positioned at a certain distance from the xe2x80x9ccuttingxe2x80x9d surface of the piece for cutting, with the direction of the cutting jet of oxygen generally being selected to being substantially perpendicular to the cutting surface to improve effectiveness (if the cutting jet of oxygen is orthogonal to the cutting surface, then the thickness of material that needs to be cut through is minimized, thereby enabling the speed of cutting to be maximized and providing savings in fluid consumption).
In general, all of the oxygen-cutting nozzles presently in use are mounted so as to move relative to the piece for cutting, above and/or below said piece, but always outside the cut slot. This constitutes a major drawback insofar as the cutting jet of oxygen needs to travel a considerable distance through the open air between leaving the oxygen-cutting nozzle and striking the surface of the metal to be cut. This drawback naturally increases with increasing thickness of the piece to be cut, and puts a de facto limit on using oxygen-cutting techniques to cutting pieces of relatively small thickness only. This drawback also applies to the heating jet which is generally restricted to heating the impact zone on the surface and/or down to a shallow depth from the surface of the piece. It is the heat given off by the spontaneous combustion of the hot metal due to the cutting oxygen that serves to generate and propagate heat along the cut slot throughout the entire thickness of the piece being cut, thus making it possible to maintain and continue the oxygen-cutting operation by spontaneous combustion using the cutting oxygen. During the cutting process, the jet of oxygen-cutting fluids emitted by the oxygen-cutting torch held at a determined height above the piece forms a slot which passes right through the thickness of the piece that is to be cut. The leading edge of the slot is then substantially rectilinear and in line with the axis of the oxygen-cutting jet, said line moving progressively during the cutting process at a speed referred to the oxygen-cutting speed, which speed corresponds to the speed of travel of the oxygen-cutting torch relative to the piece to be cut. For a nozzle having given geometrical and fluidic characteristics, the oxygen-cutting speed is a function, amongst other things, of the thickness of the piece to be cut: the greater the thickness of the piece, the slower the cutting speed because of combustion heat and combustion itself propagating along the slot from its inlet to its outlet by degrees in non-instantaneous manner.
To fill out the state of the art, mention can also be made of various oxygen-cutting methods that make use of a plurality of torches.
Thus, document U.S. Pat. No. 3,852,126 describes an oxygen-cutting method making use of two torches, a first torch having a vertical axis and a second torch having an oblique axis. That disposition is intended to enable the two torches to be brought together laterally in a direction extending transversely relative to the trajectory so that the two slots overlap in part. Nevertheless, no mention is made of moving the two torches so close together that their respective slots overlap completely, nor is there any mention of inserting one of the torches into the slot made by the other.
Document EP-A-0 017 807 describes oxygen-cutting apparatus presenting a first cutting torch having a vertical axis associated with a second torch for trimming purposes carried by a support blade that passes into the slot, the sole and unique function of the second torch being to rectify the edges of the slot on the face of the piece to be cut that is remote from its face facing the torch.
Finally, the technological background is illustrated by documents JP-A-60 052 985 and U.S. Pat. No. 3,492,552.
Document JP-60 052 985 describes a method of forming an edge with a curved groove by providing for a vertical axis torch to pass in order to obtain a straight cut followed by a torch which is transversely oblique in order to obtain a cut at 45xc2x0, and finally followed by a melting torch in order to form the concave edge. Document U.S. Pat. No. 3,492,552 describes a numerically-controlled apparatus for positioning a torch relative to a workpiece.
The invention relates more particularly to oxygen-cutting thick pieces of steel at high speed. It will be understood that existing techniques provide performance that is very limited, both as to the thickness of the piece that can be cut and as to the speed of oxygen-cutting.
The invention seeks to devise an oxygen-cutting technique that enables the above-specified drawbacks and/or limitations to be avoided.
An object of the invention is thus to provide a method and apparatus for oxygen-cutting thick pieces of steel at high speed, being capable of cutting thick pieces of steel in regular and fast manner regardless of the thickness of the piece to be cut. In particular, the looked-for technique must be capable of performing splitting operations under conditions that are technically and economically satisfactory.
According to the invention, this problem is solved by a method of oxygen-cutting a thick piece of steel at high speed in which an oxygen-cutting torch held at a determined height above the piece to be cut is moved and in which a slot torch comprising at least one blade nozzle that passes inside the oxygen-cutting slot is also moved synchronously with the movement of the oxygen-cutting torch, said blade torch emitting at least one jet of heating and/or oxygen-cutting fluids via its leading edge to strike the leading edge of the slot where they combine with the jet of oxygen-cutting fluids emitted by the oxygen-cutting torch to form a leading edge of the slot having a profile in the form of a broken line.
By using a slot torch acting from inside the oxygen cut slot, the above-mentioned drawbacks of the jet of heating and/or oxygen-cutting fluids traveling long distances is avoided, and additionally oxygen-cutting power is increased by increasing the number of oxygen-cutting nozzles if it is desired to have very high power in order to cut through thick pieces, e.g. pieces which are considerably thicker than 10 centimeters (cm). Depending on circumstances, the slot torch can be used as an injection nozzle (single or multiple), serving only to project heating fluids towards the leading edge of the slot.
Preferably, the jet from the oxygen-cutting torch extends in a direction which is substantially perpendicular to the corresponding surface of the piece to be cut, while the jet(s) from the slot torch is/are inclined at a determined acute angle relative to said direction.
Under such circumstances, and advantageously, the slot torch emits a plurality of superposed jets of heating and/or oxygen-cutting fluids engaging the leading edge of the slot at different acute angles, with the values of the angles increasing with increasing distance from the surface of the piece that is engaged by the jet from the oxygen-cutting torch. By using a plurality of superposed jets of oxygen-cutting fluids engaging the same leading edge of the slot at different acute angles, the length of the slot, i.e. the distance between its inlet and its outlet is subdivided into a plurality of segments or xe2x80x9coxygen-cutting stepsxe2x80x9d by allocating an oxygen-cutting nozzle having its own specific characteristics to each of the segments such that the speed at which the piece is cut is increased considerably, so as to reach the speed possible for a single step. This is thus the first occasion on which a genuine slot nozzle has been used within the oxygen cut slot throughout the cutting process.
Preferably, the oxygen-cutting torch and the slot torch are moved synchronously by mounting their associated supports on a common carriage moving horizontally above the piece to be cut. In particular, the oxygen-cutting and slot torches are movable vertically, the slot torch being retractable above the piece to be cut.
Provision can also be made for the slot torch to be set into vertical vibration during at least a portion of the cutting process. Imparting such vertical vibration facilitates progress of the slot blade along the cut slot as the blade advances during the cutting process.
The invention also provides apparatus for implementing the above-specified oxygen-cutting method, the apparatus being remarkable in that it comprises a horizontally displaceable carriage, said carriage carrying supports for an oxygen-cutting torch and a slot torch, the oxygen-cutting torch being vertically above the piece to be cut and being arranged to emit a substantially vertical jet of oxygen-cutting fluids, while the slot torch has at least one blade nozzle arranged to move inside the cut slot and to emit at least one inclined jet of heating and/or oxygen-cutting fluids from its leading edge.
Preferably, the supports for the oxygen-cutting and slot torches are individually adjustable in vertical position. In particular, the support for the slot torch is suspended from a vertical axis actuator, said actuator having a stroke enabling the blade nozzle(s) to be raised above the piece to be cut.
Provision may optionally be made for the cylinder of the actuator supporting the slot torch to be connected to a vibrator capable of generating low amplitude vibration in a vertical direction.
In a particular embodiment, the blade nozzle of the slot torch is a single nozzle, having a set of internal channels extending obliquely between the top facet and the leading edge of said blade nozzle. Naturally, in a variant, provision can be made for nozzles in the form of multiple blades, each being capable of emitting one or more jets of oxygen-cutting fluids.
In which case it is preferable for the internal channels to be arranged to form at least one group associated with a single jet of heating and/or oxygen-cutting fluids so as to enable the cutting oxygen and/or heating gas to be passed together with a cooling fluid. In particular, the blade nozzle has a plurality of groups of internal channels for producing superposed inclined jets, with the channels in any one group being identically inclined relative to the vertical, and with the angle of inclination increasing from one group to the next going downwards in said blade nozzle.
When the piece being cut is a continuous casting, it is advantageous to provide for the carriage supporting the oxygen-cutting and slot torches to be displaceable transversely to the continuous casting direction, being mounted on a main carriage which moves horizontally above the moving piece in the continuous casting direction, said main carriage having means for temporarily connecting it with said moving piece.